1. Technical Field
The present invention generally relates to semiconductor devices. More particularly, the present invention relates to the integration of stacked low temperature semiconductor devices with metal-oxide-semiconductor (MOS) devices and processes.
2. Description of the Related Art
The ever increasing demand of small, portable multifunctional electronic devices has led to the continued proliferation of smart phones, personal computing devices, personal audio devices (e.g., MP3 players), as well as biomedical and security devices. Such devices are expected to support and perform a greater number of increasingly complex and sophisticated functions while consuming less and less power. Such electronic devices rely on limited power sources (e.g., batteries and/or alternative energy harvesting systems) while providing ever-increasing processing capabilities and storage capacity.
Accordingly, there is a continuing trend in the semiconductor industry to manufacture not only high functionality, high-performance, low-power integrated circuits (ICs), but also low cost ICs. These goals have been achieved in large part by scaling down the semiconductor IC dimensions and stacking IC chips and thus increasing circuit densities and functionality. Achieving higher densities calls for smaller feature sizes, smaller separations between features and layers, and more precise feature shapes. The scaling down of IC dimensions and reduction of parasitic resistances and capacitances can facilitate faster circuit performance (e.g., faster switching speeds) and can lead to higher effective yield in IC fabrication processes by packing more circuits on a semiconductor die and/or more die on a semiconductor wafer. However, continued scaling also introduces considerable challenges. For example, as the minimum feature size of MOS devices has decreased, the OFF state leakage current has increased, and is rapidly approaching ON state current levels. In addition, transistor density is limited by the amount of area that is required between devices in order to electrically isolate them from each other.